1. Field of the Invention
The invention relates to a system for controlling no load operation of an internal combustion engine during idle or deceleration.
2. Description of the Prior Art
In controlling idle speed and air fuel ratio during no load operation of a carburetor injected internal combustion engine, a slow adjusting screw and/or an air adjusting screw must be carefully adjusted.
However, it is difficult to maintain the air/fuel ratio constant during no load operation, since the engine speed varies in accordance with the engine temperature during no load operation, specifically, during idle operation, and it varies among engines depending on degree of aging of the engine.
Some carburetors are provided with a fast idle mechanism or a choke mechanism. The amount of intake air and the air/fuel ratio are controlled by such mechanisms in order to stabilize the engine and to shorten the period for engine warming-up. However, these carburetor systems also have a problem in that it is impossible to control the engine speed and the air/fuel ratio to desired values.
In the case of fuel injected engines, the flow rate of the air flowing through a bypass passage bypassing a throttle valve is controlled by a bypass air adjusting screw or a temperature sensitive bypass air control valve. The quantity of fuel injected is determined on the basis of the output signal of an air flow meter which detects the quantity of the air flowing through the bypass passage. However, these engines also have a problem in that the deviations between the engine speed and the air/fuel ratio with respect to desired values grow larger when the air flow meter produces an erroneous output signal. Thus, the prior art fuel supply systems suffer from a drawback that the engine speed and the air/fuel ratio are not controlled accurately during no load engine operation.